JP2013149871A - Flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible wiring board excellent in connection reliability between conductive layers.SOLUTION: A flexible wiring board (1) of the present invention comprises: first conductive layers (12a, 12b); second conductive layers (14a, 14b) provided on the first conductive layers (12a, 12b) via an adhesive resin cured product layer (11); a through via (16) provided between the first conductive layers (12a, 12b) and the second conductive layers (14a, 14b); and a conductive particle layer (17a) which is provided so as to cover the adhesive resin cured product layer (11) in at least the through via (16) and electrically connects the first conductive layers (12a, 12b) and the second conductive layers (14a, 14b).

Description

  The present invention relates to a flexible wiring board having a via hole used for a portable terminal or the like.

  In recent years, in the field of mobile phone terminals and the like, in order to improve component mounting density, finer wiring circuits and multilayers (both sides or multilayers) have been demanded. Double-sided flexible wiring boards having a plurality of conductive layers, The ratio of multilayer flexible wiring boards is increasing. Double-sided flexible wiring boards and multilayer flexible wiring boards use via holes (plating holes) for interlayer connection of a plurality of conductive layers. Examples of via holes used for interlayer connection of double-sided flexible wiring boards and multilayer flexible wiring boards include through via holes and blind via holes.

  In the manufacturing process of a double-sided flexible wiring board or a multilayer flexible wiring board, a photolithography method using a photosensitive resin (see, for example, Patent Document 1 and Patent Document 2) or an etching method using an alkali-soluble resin (for example, a patent) Via holes are formed according to Document 3).

JP 2005-26297 A JP 2000-91743 A JP 2011-228493 A

  By the way, in the manufacturing process of a double-sided flexible wiring board or a multilayer flexible wiring board, a plurality of conductive layers are electrically connected by plating applied to the inner wall of the via hole. However, in the conventional flexible wiring board, the adhesion between the plating and the insulating layer may not always be sufficient, and the plating is peeled off from the insulating layer by bending the flexible wiring board, and the connection reliability between the plurality of conductive layers May decrease.

  This invention is made | formed in view of this point, and it aims at providing the flexible wiring board excellent in the connection reliability between conductive layers.

  The present inventors have found that the connection reliability between the conductive layers can be improved by electrically connecting the conductive layers through the conductive particle layer provided on the inner wall of the via hole, and the present invention has been completed. . That is, the present invention is as follows.

  The flexible wiring board of the present invention includes a first conductive layer, a second conductive layer provided on the first conductive layer via an adhesive resin, and between the first conductive layer and the second conductive layer. And a conductive fine particle layer provided so as to cover at least the adhesive resin in the via hole and electrically connecting the first conductive layer and the second conductive layer. It is characterized by that.

  In the flexible wiring board of the present invention, the elastic modulus of the adhesive resin is preferably 0.05 GPa or more and 3.0 GPa or less.

  In the flexible wiring board of this invention, it is preferable that the thickness of the said electroconductive particle layer is 0.01 micrometer or more and 10 micrometers or less.

  According to the present invention, a flexible wiring board having excellent connection reliability between conductive layers can be realized.

It is a cross-sectional schematic diagram of the double-sided flexible wiring board which concerns on embodiment of this invention. It is the schematic of the manufacturing process of the double-sided flexible wiring board which has a penetration via hole concerning an embodiment of the invention. It is the schematic of the manufacturing process of the double-sided flexible wiring board which has a blind via hole which concerns on embodiment of this invention. It is a cross-sectional schematic diagram of the multilayer flexible wiring board which concerns on this Embodiment. It is the elements on larger scale of the rigid part of the multilayer flexible wiring board concerning this Embodiment. It is the schematic of the manufacturing process of the multilayer flexible wiring board which concerns on this Embodiment.

  A flexible wiring board according to an embodiment of the present invention includes a first conductive layer, a second conductive layer provided on the first conductive layer via an adhesive resin cured material layer containing an alkali-soluble resin, The conductive fine particle layer is provided so as to cover at least the cured adhesive resin in the via hole and electrically connects the first conductive layer and the second conductive layer.

  In the present embodiment, a conformal mask is formed on the conductive layer provided on the uncured adhesive resin layer, and via holes (through via holes and / or blinds) are formed in the uncured adhesive resin layer via the conformal mask. Via hole). Then, after the conductive particle layer is formed in the via hole, the conductive layers formed on both main surfaces of the uncured adhesive resin layer are electrically connected by performing electroplating in the via hole.

  In this embodiment, by using a cured adhesive resin layer containing an alkali-soluble resin, via holes (through via holes and blind via holes) are efficiently formed by dissolving and removing the cured adhesive resin layer using an alkaline aqueous solution. it can. In addition, since the conductive layer is formed, the first conductive layer and the second conductive layer can be electrically connected in a short time without being exposed to harsh chemical treatment conditions. High reliability can be obtained in simplification, reduction of manufacturing cost, and circuit connection between adhesive resin cured product layers.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a double-sided flexible wiring board according to an embodiment of the present invention. As shown in FIG. 1, a double-sided flexible wiring board 1 according to the present embodiment is provided on an adhesive resin cured product layer 11 containing an alkali-soluble resin and one main surface of the adhesive resin cured product layer 11. Conductive layer 12a (first conductive layer), conductive layer 12b (second conductive layer) provided on the other main surface of the cured adhesive resin layer 11, and conductive layers 12a and 12b. And a through via hole 13 provided therebetween. The through via hole 13 is provided so as to penetrate the cured adhesive resin layer 11 and the conductive layers 12 a and 12 b, and the conductive layer 12 a and the conductive layer 12 b are electrically connected through the through via hole 13.

  A conductive particle layer 13 a containing conductive particles is provided on the inner wall of the through via hole 13 so as to cover at least the adhesive resin cured product layer 11 in the through via hole 13. The conductive particle layer 13a is provided so that a part thereof is in contact with the conductive layer 12a and the conductive layer 12b, and the conductive layer 12a and the conductive layer 12b are electrically connected via the conductive particle layer 13a. Is done. Here, the cured adhesive resin layer 11 in the through via hole 13 only needs to be covered with the conductive particle layer 13a so that at least the conductive layer 12a and the conductive layer 12b are electrically connected. On the conductive particle layer 13a, plating 13b is provided so as to cover the inner wall of the through via hole 13.

  The cured adhesive resin layer 11 functions as an adhesive layer that insulates the conductive layers 12a and 12b and insulates the conductive layers 12a and 12b. In the flexible wiring board 1, since the cured adhesive resin layer 11 contains an alkali-soluble resin, it is possible to form the through via hole 13 by dissolving and removing the cured adhesive resin layer 11 with an alkaline solution. The conductive layers 12a and 12b are made of a conductive member such as a copper foil, for example. In addition, as a material which comprises the conductive layers 12a and 12b, there will be no restriction | limiting in particular if the adhesiveness with the adhesive resin hardened | cured material layer 11 is acquired.

  As the conductive particles of the conductive particle layer 13a, for example, carbon-based fine particles, metal-based fine particles, and the like can be used. Carbon black particles, carbon nanofibers and the like can be used as the carbon-based fine particles. Metal oxide particles include composite oxide particles of indium oxide and tin oxide (ITO particles), composite oxide particles of tin oxide and phosphorus oxide (PTO particles), and metal oxide particles such as silver oxide particles. Can be mentioned. These electroconductive particles may be used independently and may use 2 or more types together. Among these conductive particles, carbon black particles are preferable from the viewpoint of convenience and price.

  In the present embodiment, as will be described in detail later, the alkali-soluble resin contained in the adhesive resin cured product layer 11 has a functional group such as a phenolic hydroxyl group or a carboxyl group. Due to the interaction with the conductive fine particles, the adherence to the conductive fine particles to the adhesive resin cured product layer 11 is improved. Thereby, since the adhesiveness of the electroconductive particle layer 13a and the adhesive resin hardened material layer 11 improves, peeling of the electroconductive particle layer 13a from the adhesive resin hardened material layer 11 can be prevented, and double-sided flexible wiring The connection reliability of the plate 1 is improved.

  As an average particle diameter of electroconductive particle, the thing within the range of 10 nm-1 micrometer can be used, for example. The average particle size of the conductive particles is preferably 10 nm or more from the viewpoint of preventing detachment that causes insulation failure when the conductive particle layer 13a is formed. From the viewpoint of easy availability and easy use, 1 μm The following is preferable. The average particle size is preferably 10 nm to 400 nm, more preferably 10 nm to 100 nm. In addition, when carbon black particles are used as the conductive particles, those having a large specific surface area and a small aspect ratio have good adhesion to the inner wall of the via hole, coverage, and conductivity when the conductive layer 12a is formed. preferable.

  In the present embodiment, since the conductive layers 12a and 12b are electrically connected through the conductive particle layer 13a, even when the vicinity of the through via hole 13 of the flexible wiring board 1 is bent, the cured adhesive resin The conductive particles follow the layer 11 and the conductive layers 12a and 12b. Thereby, since peeling of the electroconductive particle layer 13a from the adhesive resin hardened material layer 11 and the electroconductive layers 12a and 12b can be suppressed, the connection reliability between the electroconductive layers 12a and 12b is improved. Moreover, even when the temperature in the usage environment of the flexible wiring board 1 changes, the conductive particles follow the cured adhesive resin layer 11 and the conductive layers 12a and 12b which are deformed by thermal expansion and contraction. Therefore, even when a temperature change occurs, peeling of the conductive particle layer 13a from the adhesive resin cured product layer 11 and the conductive layers 12a and 12b can be suppressed, so that the connection reliability of the flexible wiring board 1 is improved. Further, by electrically connecting the conductive layers 12a and 12b with the conductive particle layer 13a, the conductive layers 12a and 12b can be electrically connected without performing electroless plating. 11 is not exposed to the chemical treatment of electroless plating. Therefore, alteration of the adhesive resin cured material layer 11 due to chemical treatment can be prevented.

  In addition, the thickness of the conductive particle layer 13a is preferably in the range of 0.01 μm or more and 10 μm or less. When the thickness of the conductive particle layer 13a is 10 μm or less, the detachment of the conductive particle layer 13a and the formation of irregularities on the inner wall of the via hole during electrolytic plating can be suppressed. Further, if the thickness of the conductive particle layer 13a is 0.01 μm or more, the conductive particle layer 13a can be formed uniformly, so that the conduction failure between the conductive layers 12a and 12b can be reduced and the conductive layers 12a and 12b can be reduced. Connection reliability is improved. Further, the thickness of the conductive particle layer 13a is preferably 0.05 μm or more and 10 μm or less, and more preferably 0.2 μm or more and 2 μm or less.

  The thickness of the conductive particle layer 13a formed in the via hole is determined by scanning the flexible wiring board 1 after embedding the flexible wiring board 1 with an epoxy resin and performing sample processing by FIB (Focused Ion Beam) in a cross-sectional direction passing through the center of the via hole. It can be obtained by measurement by observation with a scanning electron microscope (SEM).

  Next, a method for manufacturing the flexible wiring board 1 according to the present embodiment will be described. Below, the manufacturing method of the double-sided flexible wiring board which has a penetration via hole as a via hole, and the manufacturing method of the double-sided flexible wiring board 1 which has a blind via hole are demonstrated. In the following description, the uncured adhesive resin layer and the cured adhesive resin layer are given the same reference numerals (uncured adhesive resin layer 11 '' or cured adhesive resin layer 11). To explain.

  FIG. 2 is a schematic view of a manufacturing process of the double-sided flexible wiring board 1 having the through via hole 13. First, copper foil is laminated on both main surfaces of an uncured adhesive resin layer 11 'provided by applying and drying an adhesive resin varnish to provide conductive layers 12a and 12b (see FIG. 2A). Next, a dry film (not shown) is laminated on the conductive layers 12a and 12b, and a part of the conductive layers 12a and 12b is removed by exposure / development and etching to form a conformal mask 14 (see FIG. 2B). ). In this step, it is desirable to minimize the displacement of the etching portions of the conductive layers 12a and 12b (for example, 20 μm or less when the diameter of the through via hole 13 to be formed is 100 μm).

  Next, the uncured adhesive resin layer 11 ′ exposed by removing the conductive layers 12 a and 12 b is dissolved and removed with an alkaline solution to form the through via hole 13 (see FIG. 2C). The alkaline liquid is not particularly limited as long as it can dissolve and remove the uncured adhesive resin layer 11 'containing an alkali-soluble resin. As the alkaline solution, for example, an aqueous sodium carbonate solution, an aqueous sodium hydroxide solution, or an aqueous potassium hydroxide solution can be used. The uncured adhesive resin layer 11 ′ can be dissolved and removed with an alkali solution using an alkali spray device or the like used in a general flexible wiring board manufacturing process.

  Next, the uncured adhesive resin layer 11 ′ is cured by heating at 150 ° C. to 200 ° C. for 10 minutes to 5 hours using a drying furnace to obtain a cured adhesive resin layer 11. Next, after the adhesive resin hardened material layer 11 is immersed in a dispersion of conductive fine particles to adhere the conductive fine particles to the adhesive resin hardened material layer 11 on the inner wall of the through via hole 13, for example, sulfuric acid / hydrogen peroxide The solvent of the dispersion is removed with an acidic aqueous solution such as an aqueous copper sulfate solution to form the conductive particle layer 13a (see FIG. 2D). Here, the conductive particle layer 13a is formed so as to cover the adhesive resin cured material layer 11 by the interaction between the adhesive resin cured material layer 11 and the conductive particles, and a part of the conductive particle layer 13a is the conductive layer 12a. , 12b.

Next, electrolytic copper plating is performed on the inner wall of the through via hole 13 so as to cover the conductive particle layer 13a to form a plating 13b (see FIG. 2E). Next, a double-sided flexible wiring board is manufactured by forming a circuit pattern on the conductive layers 12a and 12b by a subtractive method (see FIG. 2F).

  FIG. 3 is a schematic view of a manufacturing process of a double-sided flexible wiring board having blind via holes. First, copper foil is laminated on both main surfaces of an uncured adhesive resin layer 21 'provided by applying and drying an adhesive resin varnish to provide conductive layers 22a and 22b (see FIG. 3A). Next, a dry film (not shown) is laminated on the conductive layers 22a and 22b, and a part of the conductive layers 22a and 22b is removed by exposure / development and etching to form a conformal mask 23 (see FIG. 3B). ). In this step, it is desirable to minimize the displacement of the etching portions of the conductive layers 22a and 22b (for example, 20 μm or less when the diameter of the blind via hole 24 to be formed is 100 μm).

  Next, the uncured adhesive resin layer 21 ′ exposed in the region where the conductive layers 22a and 22b are removed through the conformal mask 23 is dissolved and removed with an alkaline solution to form the blind via hole 24 (see FIG. 3C). . The alkaline liquid is not particularly limited as long as it can dissolve and remove the uncured adhesive resin layer 21 'containing an alkali-soluble resin. As the alkaline solution, for example, an aqueous sodium carbonate solution, an aqueous sodium hydroxide solution, or an aqueous potassium hydroxide solution can be used. For the dissolution and removal of the uncured adhesive resin layer 21 ′ with an alkali solution, an alkali spray device or the like used in a general flexible wiring board manufacturing process can be used. Next, by heating for 10 minutes to 2 hours at 150 ° C. to 200 ° C. using a drying furnace, the alkali-soluble resin of the uncured adhesive resin layer 21 ′ is cured and the cured adhesive resin layer 21 and To do.

  Next, the adhesive resin hardened material layer 21 is immersed in the dispersion of conductive fine particles to adhere the conductive fine particles to the adhesive resin hardened material layer 21 on the inner wall of the blind via hole 24, and then the solvent of the dispersion in an acidic aqueous solution. Is removed to form a conductive particle layer 24a (see FIG. 3D). Here, the conductive particle layer 24a is formed so as to cover the adhesive resin cured material layer 21 by the interaction between the adhesive resin cured material layer 21 and the conductive particles, and a part of the conductive particle layer 24a is formed in the conductive layer 22a. , 22b. As a result, the conductive layers 22a and 22b are electrically connected via the conductive particle layer 13a.

  Next, electrolytic copper plating is applied to the inner wall of the blind via hole 24 so as to cover the conductive particle layer 24a to form a plating 24b (see FIG. 3E). Next, a double-sided flexible wiring board is manufactured by forming a circuit pattern on the conductive layers 22a and 22b by a subtractive method (see FIG. 3F).

  Thus, in the manufacturing method of the flexible wiring board, the adhesive resin cured material layers 11 and 21 are dissolved and removed by the alkaline solution via the conformal masks 14 and 23 to the adhesive resin cured material layers 11 and 21. This makes it possible to form the via holes (through via hole 13 and blind via hole 24), so that it is possible to suppress the occurrence of smear due to the formation of the via hole. Further, since the via holes can be formed in a short time by dissolving and removing the cured adhesive resin layers 11 and 21, continuous production of double-sided flexible wiring boards is also possible. Thereby, the double-sided flexible wiring board which is excellent in production efficiency and excellent in circuit quality can be manufactured. Further, since the conductive layers 12a and 12b can be electrically connected without performing electroless plating, the cured adhesive resin layers 11 and 21 are not exposed to the chemical treatment of electroless plating. Accordingly, it is possible to prevent the adhesive resin cured material layers 11 and 21 from being deteriorated by the chemical treatment.

  Next, the multilayer flexible wiring board according to the present embodiment will be described. FIG. 4 is a schematic cross-sectional view of the multilayer flexible wiring board 100 according to the present embodiment. FIG. 5 is a partially enlarged view of the rigid portion 100a of the multilayer flexible wiring board shown in FIG. As shown in FIG. 4, the multilayer flexible wiring board 1 according to the present embodiment includes a rigid part 100a provided at both end parts on which various electronic components are mounted, and a flexible part provided between the rigid parts 100a and having flexibility. 100b.

  The rigid portion 100a includes a pair of internal conductive layers 102a and 102b (first conductive layers) provided on both main surfaces of the cured adhesive resin layer 101 containing an alkali-soluble resin, and the internal conductive layers 102a and 102b. A pair of external conductive layers 104a and 104b (second conductive layer) provided via an adhesive resin cured product 103 (adhesive resin cured product layers 103a and 103b) containing an alkali-soluble resin, and a pair of external conductive layers 104a and 104b, and a cover coat 105 provided so as to cover a part. Adhesive resin cured product 103 (adhesive resin cured product layers 103a and 103b) is an adhesive layer that adheres between internal conductive layer 102a and external conductive layer 104a and between internal conductive layer 102b and external conductive layer 102b. It functions as an insulating layer that insulates between the internal conductive layer 102a and the external conductive layer 104a and between the internal conductive layer 102b and the external conductive layer 102b. The cured adhesive resin 103 is made of the same material as the above-described cured adhesive resin layers 11, 21, 101.

  A through via hole 106 is provided between the pair of internal conductive layers 102 a and 102 b so as to penetrate the internal conductive layers 102 a and 102 b and the cured adhesive resin layer 101. The internal conductive layers 102 a and 102 b are electrically connected through the through via hole 106. The through-via hole 106 is filled with an adhesive resin cured product 103. The through via hole 106 is not necessarily filled with the cured adhesive resin 103.

  Blind via holes 107 are provided between the internal conductive layer 102a and the external conductive layer 104a and between the internal conductive layer 102b and the external conductive layer 104b. The internal conductive layer 102a and the external conductive layer 104a and the internal conductive layer 102b and the external conductive layer 104b are electrically connected through a blind via hole 107. The blind via hole 107 is filled with a cover coat 105. The blind via hole 107 may be filled with an adhesive resin 103.

  As shown in FIG. 5, a plating 106b is provided on the inner wall of the through via hole 106 via a conductive particle layer 106a. The conductive particle layer 106a is provided so as to cover the cured adhesive resin 103 in the through via hole 106, and a part of the conductive particle layer 106a is provided in contact with the internal conductive layers 102a and 102b. The internal conductive layers 102a and 102b are electrically connected through the conductive particle layer 106a. The conductive particle layer 106 a is configured to include, for example, carbon black particles and the like, and has high adhesion to the cured adhesive resin layer 101. For this reason, by providing the plating 106b through the conductive particle layer 106a, it is possible to prevent other components from being mixed between the cured adhesive resin layer 101 and the conductive particle layer 106a.

  On the inner wall of the blind via hole 107, a plating 107b is provided via a conductive particle layer 107a. The conductive particle layer 107a is provided so as to cover the adhesive resin cured product 103 in the blind via hole 107, and a part of the conductive particle layer 107a is provided in contact with the internal conductive layers 102a and 102b and the external conductive layers 104a and 104b. . The internal conductive layers 102a and 102b are electrically connected through the conductive particle layer 106a. The internal conductive layer 102a and the external conductive layer 104a and the internal conductive layer 102b and the external conductive layer 104b are electrically connected through the conductive particle layer 107a. The conductive particle layer 107 a includes, for example, carbon black particles and has high adhesion with the adhesive resin 103. For this reason, by providing the plating 107b through the conductive particle layer 107a, mixing of other components between the adhesive resin 103 and the conductive particle layer 107a can be prevented. The blind via hole 107 may be filled with a cover coat 105. The blind via hole 107 may be filled with an adhesive resin 103.

  In the present embodiment, the alkali-soluble resin contained in the cured adhesive resin layer 101 and the cured adhesive resin layer 103 has a high functional group such as a phenolic hydroxyl group or a carboxyl group, as will be described in detail later. Therefore, the adhesion between the functional groups and the conductive particles improves the adhesiveness of the adhesive resin cured product layer 101 and the adhesive resin cured product 103 to the conductive fine particles. As a result, the adhesion between the conductive particle layers 106a and 107a and the cured adhesive resin layer 101 and the cured adhesive resin 103 is improved. The peeling of the conductive particle layer 13a can be prevented, and the connection reliability of the multilayer flexible wiring board 100 is improved.

  The flexible part 100b has an internal conductive layer 102a provided on one main surface of the cured adhesive resin layer 101, and an adhesive resin 103a provided so as to cover the internal conductive layer 102a. The internal conductive layer 102a of the flexible part 100b is provided so as to extend to the rigid parts 100a on both end sides, and the internal conductive layer 102b and the external conductive layers 104a and 104b of the rigid part 100a through the through via hole 106 and the blind via hole 107. And electrically connected.

Next, the manufacturing method of the multilayer flexible wiring board 1 which concerns on this Embodiment is demonstrated.
The manufacturing method of the multilayer flexible wiring board 100 according to the present embodiment includes the steps of providing the first conductive layers 102a and 102b on the adhesive resin cured product layer 101, and the internal conductive layers 102a and 102b (first conductive layer). A step of providing external conductive layers 104a and 104b (second conductive layer) via an adhesive resin 103 containing alkali-soluble resin, a step of forming a conformal mask on the external conductive layers 104a and 104b, and a conformal mask. The adhesive resin 103 is dissolved and removed to form the blind via hole 107, the adhesive resin 103 is heated and cured, and the blind via hole 107 is plated 107a to form the internal conductive layers 102a and 102b and the external conductive layer. A step of electrically connecting the layers 104a and 104b and a circuit to the external conductive layers 104a and 104b. And a step of forming a turn, the.

  Hereinafter, each step will be described in detail with reference to FIG. FIG. 6 is a schematic view of a manufacturing process of the multilayer flexible wiring board 1 according to the present embodiment.

  First, an adhesive resin varnish containing an alkali-soluble resin is applied and dried to provide an uncured adhesive resin cured product layer 101 ′, and copper foil is laminated on both main surfaces of the uncured adhesive resin layer 101 ′. Then, the internal conductive layers 102a and 102b are provided. As the adhesive resin varnish used for the uncured adhesive resin layer 101, the same adhesive resin varnish as that used for the adhesive resin cured product 103 can be used. Next, after laminating a dry film (not shown) on the internal conductive layers 102a and 102b, a part of the internal conductive layers 102a and 102b is removed by exposing and developing the dry film and etching the internal conductive layers 102a and 102b. To form a conformal mask (not shown). Next, the through-cured via hole 106 is formed by dissolving and removing the uncured adhesive resin layer 101 ′ exposed in the etching regions of the internal conductive layers 102 a and 102 b with an alkaline solution through a conformal mask. The uncured adhesive resin layer 101 ′ can be dissolved and removed under the same conditions as those described with reference to FIGS. 2 and 3. Next, by using a drying furnace and heating at 150 ° C. to 200 ° C. for 10 minutes to 2 hours, the alkali-soluble resin of the uncured adhesive resin layer 101 ′ is cured to form a cured adhesive resin layer 101. .

  Next, the adhesive resin cured product layer 101 is immersed in the dispersion of conductive fine particles to adhere the conductive fine particles to the adhesive resin cured product layer 101 on the inner wall of the through via hole 106, and then the solvent of the dispersion in an acidic aqueous solution. Then, a conductive particle layer 106a (not shown in FIG. 6, refer to FIG. 5) is formed. Here, the conductive particle layer 106a is formed so as to cover the cured adhesive resin layer 101 by the interaction between the cured adhesive resin layer 101 and the conductive particles, and a part of the conductive particle layer 106a is internally conductive. Contact the layers 102a, 102b. As a result, the internal conductive layers 102a and 102b are electrically connected through the conductive particle layer 106a.

  Next, a double-sided flexible wiring board 110 as a core substrate is manufactured by forming a circuit pattern on the internal conductive layers 102a and 102b by a subtractive method or the like (see FIG. 6A). The internal conductive layers 102a and 102b may be electrically connected through blind via holes. Moreover, the multilayer flexible wiring board 1 can be manufactured even if a single-sided flexible wiring board or a multilayer flexible wiring board is used as the core substrate. Moreover, you may manufacture a multilayer flexible wiring board using the double-sided flexible wiring board shown in FIG.2 and FIG.3.

  Next, an adhesive resin varnish is applied and dried on the internal conductive layers 102a and 102b of the double-sided flexible wiring board 110 to provide uncured adhesive resin layers 103a 'and 103b'. The uncured adhesive resin layers 103a 'and 103b' here are in an uncured state or a semi-cured state. Next, a copper foil is laminated via the uncured adhesive resin layers 103a 'and 103b' to provide external conductive layers 104a and 104b (see FIG. 6B). Here, the uncured adhesive resin 103 ′ is filled in the through via hole 106 of the double-sided flexible wiring board 110. Here, the external conductive layers 104a and 104b may be laminated after the uncured adhesive resin 103 ′ is applied on the internal conductive layers 102a and 102b, and the uncured on the copper foils (external conductive layers 104a and 104b). You may laminate the resin-coated copper foil which apply | coated adhesive resin 103 'on the internal conductive layers 102a and 102b, respectively. The external conductive layers 104a and 104b can be laminated at 50 ° C. to 140 ° C., preferably 70 ° C. to 120 ° C., more preferably 90 ° C. to 110 ° C. by using a vacuum press or a vacuum laminator.

  Next, after the dry film 108 is laminated on the external conductive layers 104a and 104b, a part of the external conductive layers 104a and 104b is exposed by exposure and development of the dry film 108 (see FIG. 6C). Subsequently, the external conductive layers 104a and 104b are etched to remove a part of the external conductive layers 104a and 104b to form a conformal mask, and the external conductive layer 104b in a region to be the flexible portion 100b is removed (see FIG. 6D).

  Next, the uncured adhesive resin layers 103a ′ and 103b ′ exposed in the etching regions of the external conductive layers 104a and 104b are dissolved and removed with an alkaline solution through a conformal mask to form the blind via hole 107 and the alkali The dry film 108 is peeled off with the solution. Further, the uncured adhesive resin layers 103a 'and 103b' in the region to be the flexible portion 100b are also dissolved and removed (FIG. 6E). Thus, since the formation of the blind via hole 107 and the peeling of the dry film 108 can be performed with an alkaline solution, the production efficiency can be improved and the cost of forming the via hole can be reduced. As the alkaline solution, for example, a 3% by mass sodium hydroxide aqueous solution which is a dry film peeling solution can be used.

  Next, using a drying furnace, the uncured adhesive resin layers 103a 'and 103b' are heated and cured to form the cured adhesive resin layers 103a and 103b. The heat curing is preferably performed at a temperature of 120 ° C. or higher and 400 ° C. or lower from the viewpoint of reactivity of the uncured adhesive resin layers 103a ′ and 103b ′. More preferably, it is 150 degreeC or more and 250 degrees C or less.

  The reaction atmosphere in heat curing can be carried out in an air atmosphere or an inert gas atmosphere. In order to suppress the oxidation of a conductive layer, it is preferable that it is under nitrogen stream at high temperature. The time required for heat curing varies depending on the reaction conditions, but is usually within 24 hours, particularly preferably in the range of 0.1 to 8 hours.

  Next, the conductive particles are adhered to the adhesive resin 103 in the blind via hole 107 to the conductive fine particle dispersion, and then the solvent of the dispersion is removed with an acidic aqueous solution to remove the conductive particle layer 107a (not shown in FIG. 6). As shown in FIG. Here, the conductive particle layer 106a is formed so as to cover the adhesive resin cured product 103 by the interaction between the cured adhesive resin product 103 and the conductive particles, and a part of the conductive particle layer 106a is formed in the internal conductive layer 102a. , 102b and the outer conductive layers 104a, 104b. As a result, the internal conductive layer 102a and the external conductive layer 104a and the internal conductive layer 102b and the external conductive layer 104b are electrically connected through the conductive particle layer 107a (see FIG. 6F).

  Next, the external conductive layers 104a and 104b are patterned by a subtractive method to form a circuit (see FIG. 6G). Next, in the same manner as in the conventional method for manufacturing a wiring board of a flexible substrate, surface treatment such as formation of a cover coat 105 is performed to manufacture a multilayer flexible wiring board 100 (see FIG. 6H).

  As described above, in the method for manufacturing the multilayer flexible wiring board 100, the uncured adhesive resin layers 103a ′ and 103b ′ are dissolved and removed by the alkaline solution through the conformal mask. Can be suppressed. In addition, since the uncured adhesive resin layers 103 a ′ and 103 b ′ and the dry film resist 108 can be dissolved and removed together with an alkaline solution, the manufacturing process of the multilayer flexible wiring board 100 can be simplified. In addition, since the inner conductive layers 102a and 102b and the outer conductive layers 104a and 104b can be electrically connected without performing electroless plating, the cured adhesive resin layers 103a and 103b are exposed to a chemical treatment for electroless plating. There is nothing. Therefore, alteration of the adhesive resin cured product layers 103a and 103b due to the chemical treatment can be prevented.

  The cured adhesive resin layer 101 and the cured adhesive resin layers 103a and 103b are for imparting flexibility to the flexible portion 100b of the multilayer flexible wiring board 100 and for enabling molding by a roll-to-roll method. It is preferable that the elastic modulus is low.

  Next, an adhesive resin varnish containing an alkali-soluble resin used for the flexible wiring board according to the present embodiment will be described. Here, the adhesive resin cured product layer 101 and the adhesive resin cured product layers 103a and 103b of the multilayer flexible wiring board 100 shown in FIG. 4 will be described as an example, but the double-sided flexible wiring board shown in FIGS. It is possible to use the same alkali-soluble resin in the one adhesive resin cured product layer 11, 21.

  The adhesive resin varnish is not particularly limited as long as it contains an alkali-soluble resin that is dissolved by a dissolution treatment with an alkaline solution after forming a conformal mask. Further, as an alkali-soluble resin, an uncured adhesive resin layer 101 having a film thickness of 25 μm and uncured adhesive resin layers 103a ′ and 103b ′ are formed by using an adhesive resin varnish, and dissolved in an aqueous sodium hydroxide solution. The speed is preferably 0.30 μm / sec or more. The above physical properties are measured using an uncured adhesive resin layer 101 ′ and uncured adhesive resin layers 103a ′ and 103b ′ obtained after applying an adhesive resin varnish on a conductive film and removing the solvent by heating. To do. If the alkali dissolution rate of the uncured adhesive resin layer 101 ′ and the uncured adhesive resin layers 103a ′ and 103b ′ is within the above range, the uncured adhesive resin layer 101 ′ and the uncured adhesive resin layer 103a ′, The alkali solubility of 103b ′ can be easily controlled, and an alkaline liquid spray device generally used in the manufacturing process of a flexible printed wiring board can be used.

  Further, the dissolution rate of the cured adhesive resin layer 101 and the cured adhesive resin layers 103, 103b obtained by heating the uncured adhesive resin layer at 150 ° C. or higher in an aqueous sodium hydroxide solution is 0.05 μm / sec or less, and the elastic modulus is preferably 0.05 GPa or more and 3.0 GPa or less. If the elastic modulus of the adhesive resin cured product layer 101 and the adhesive resin cured product layers 103 and 103b is 3.0 GPa or less, the warp of the multilayer flexible wiring board 100 can be reduced and the flexibility is improved. Further, if the elastic modulus of the adhesive resin cured product layer 101 and the adhesive resin cured product layers 103 and 103b is 0.5 GPa or more, the stress of the adhesive resin cured product layer 101 and the adhesive resin cured product layers 103a and 103b. It is effective in mitigation and improves adhesion of conductive particles to the adhesive resin cured product layer 101 and adhesive resin cured product layers 103a and 103b in the inner wall of the via hole (through via hole 106 and blind via hole 107), and is flexible in multiple layers. Connection reliability between the inner conductive layers 102a and 10b and the outer conductive layers 104a and 104b of the wiring board 100 is improved. More preferably, it is 0.05 GPa or more and 1.5 Gpa or less. Furthermore, as the adhesive resin cured product layers 103a and 103b, a glass transition point temperature of 150 ° C. or lower, preferably 50 ° C. to 120 ° C., is preferable because lamination can be performed using a general laminating apparatus.

  The alkali-soluble resin is preferably a carboxyl group-containing resin or a hydroxyl group-containing resin in the molecular chain because it has alkali solubility. Among these, a phenolic hydroxyl group-containing resin is more preferable because of excellent reactivity with a crosslinking agent during heat curing.

  Examples of the alkali-soluble resin include novolak resin, acrylic resin, copolymer of styrene and acrylic acid, polymer of hydroxystyrene, polyvinylphenol, poly α-methylvinylphenol, polyimide resin, polybenzoxazole resin, polyvinyl Examples thereof include a phenol resin, a resole resin, a copolymer of an acrylic acid derivative having a phenolic hydroxyl group, and a polyvinyl acetal resin having a phenolic hydroxyl group. Of these, polyvinylphenol resins, novolak resins, and polyimide resins having phenolic hydroxyl groups are preferred.

  Examples of the polyvinylphenol resin include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene, trihydroxystyrene, tetrahydroxystyrene, pentahydroxystyrene, 2- (o-hydroxyphenyl) propylene, 2- Examples include resins obtained by polymerizing hydroxystyrenes such as (m-hydroxyphenyl) propylene and 2- (p-hydroxyphenyl) propylene alone or in the presence of a radical polymerization initiator or a cationic polymerization initiator. . The polyvinyl phenol resin preferably has a polystyrene-equivalent weight average molecular weight (MW) of 500 to 100,000 as measured by gel permeation chromatography, and more preferably 1,000 to 50,000.

  Examples of novolak resins include phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, propylphenol. , N-butylphenol, t-butylphenol, 1-naphthol, 2-naphthol, 4,4′-biphenyldiol, bisphenol-A, pyrocatechol, resorcinol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, phloroglucinol And at least one selected from the group consisting of phenols such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, furfural and the like aldehydes (in addition to formaldehyde) Laformaldehyde may be used, and paraaldehyde may be used instead of acetaldehyde.), Or at least one selected from the group consisting of ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, in the presence of an acid catalyst. And a resin condensed by polycondensation. Among these, phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol as phenols and formaldehyde, acetaldehyde, propionaldehyde as aldehydes or ketones The polycondensate is preferred. In particular, the mixing ratio of m-cresol: p-cresol: 2,5-xylenol: 3,5-xylenol: resorcinol is 40 to 100: 0 to 50: 0 to 20: 0 to 20: 0 to 20 in molar ratio. A polycondensate of mixed phenols or mixed phenols of phenol: m-cresol: p-cresol with a molar ratio of 1-100: 0 to 70: 0-60 and formaldehyde is preferable.

  From the viewpoint of improving the embedding property by lowering the melt viscosity, the novolak resin includes 4,4′-biphenylylene group, 2,4′-biphenylylene group, 2,2′-biphenylylene group, 1,4-xylylene in the molecule. A novolak resin having both a polymer unit of a phenol resin containing a crosslinking group such as a group, 1,2-xylylene group or 1,3-xylylene group and a phenol resin containing a methylene crosslinking group is also preferred.

  The novolak resin preferably has a polystyrene-equivalent weight average molecular weight (MW) of 500 to 15,000 as measured by gel permeation chromatography, more preferably 1,000 to 10,000. Furthermore, from the viewpoint of heat resistance and flexibility of the cured adhesive resin layers 103a and 103b obtained after heating at 200 ° C. or lower, a carboxyl group-containing polyimide, a carboxyl group-containing polyimide precursor, a phenolic hydroxyl group-containing polyimide, a phenolic hydroxyl group Preferred are polyimide containing precursors, carboxyl group-containing polybenzoxazoles, and carboxyl group-containing polybenzoxazole precursors. Among these, a phenolic hydroxyl group-containing polyimide is more preferable.

  The polyimide described above can be obtained by reacting acid dianhydride and diamine to synthesize polyamic acid (polyimide precursor) and then imidizing by heating. The polyimide described above can also be obtained by synthesizing polyamic acid (polyimide precursor) by reacting acid dianhydride and diamine, and then imidizing (chemical imidization) after adding a catalyst. it can. Among these, chemical imidation is preferable in that imidization can be completed at a lower temperature.

  Hereinafter, polyimide will be described in detail. Examples of the polyimide include those shown in the following embodiments.

(First embodiment)
The polyimide having a phenolic hydroxyl group according to the first embodiment is an alkali-soluble siloxane polyimide having a structure represented by the following general formula (1) to the following general formula (3). In this alkali-soluble siloxane polyimide, the residue from which the carboxyl group anhydride is removed is represented by the following general formula (2), and the residue from which the amino group is removed is represented by the following general formula (3). It is obtained by reacting the diamine represented.

(Second Embodiment)
The polyimide according to the second embodiment is an alkali-soluble polyimide including a structure represented by the following general formula (4) and the following general formula (5). This alkali-soluble polyimide is obtained by reacting a tetracarboxylic dianhydride represented by the following general formula (6) with a diamine in which the residue from which the amino group has been removed is represented by the following general formula (5). can get.

Examples of the tetracarboxylic dianhydride used for synthesis of the alkali-soluble polyimide according to the first embodiment, in the general formula (2), R ₁ is independently from each other, the number 1 to number 30 carbon atoms It is a monovalent hydrocarbon group. Examples of R ₁ include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; aryl groups such as phenyl groups; benzyl groups, Examples include aralkyl groups such as phenethyl group; alkenyl groups such as vinyl group, allyl group, propenyl group, isopropenyl group, and butenyl group. Among these, from the viewpoint of easy availability of raw materials, R ₁ is preferably a methyl group, an ethyl group, a phenyl group, or a vinyl group.

Examples of R ₂ include a residue obtained by removing a carboxyl group anhydride from an alkyl succinic anhydride such as propyl succinic anhydride, norbornyl anhydride, propyl nadic acid anhydride, and the like. Among these, a residue obtained by removing a carboxyl group anhydride from propyl succinic anhydride, norbornyl anhydride, or propyl nadic acid anhydride is preferable. n is an integer of 1 to 50, preferably 3 to 30, and more preferably 5 to 15. n may be the same or different. Examples of such tetracarboxylic dianhydrides include tetracarboxylic dianhydrides having a silicone chain represented by the following formula group (7).

  As content of the tetracarboxylic dianhydride component which has a silicone chain in the polyimide which has a phenolic hydroxyl group, it is preferable that it is 40 mass% or more, and it is more preferable that it is 60 mass% or more.

  A polyimide obtained using an acid anhydride having a silicone chain is excellent in alkali dissolution rate and low warpage. Moreover, it can superpose | polymerize using the polymerization solvent which does not have an amide structure excellent in drying property.

  Examples of the diamine in which the residue from which the amino group has been removed are represented by the above general formula (3) include 4,4′-diaminobiphenyl-3,3′-diol, 2,2′-bis (3-amino-4- Hydroxyphenyl) hexafluoropropane. Among these, 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane is particularly preferable.

  Examples of the tetracarboxylic dianhydride represented by the general formula (6) used for the synthesis of the alkali-soluble polyimide according to the second embodiment include 3,3 ′, 4,4′-biphenyltetracarboxylic acid dihydrate. Anhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone Tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 3,3′-oxydiphthalic dianhydride, 4,4′-oxydiphthalic dianhydride, bis (3 , 4-dicarboxyphenyl) sulfone dianhydride, polydimethylsiloxane-containing acid dianhydride, and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  Examples of the diamine in which the residue from which the amine group has been removed are represented by the above general formula (5) include 4,4′-diaminobiphenyl-3,3′-diol and 3,3′-diaminobiphenyl-4,4′-. Diol, 4,3′-diaminobiphenyl-3,4′-diol, 4,4′-diaminobiphenyl-3,3 ′, 5,5′-tetraol, 3,3′-diaminobiphenyl-4,4 ′ , 5,5′-tetraol, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 2,2′-bis (3-amino-2,4-dihydroxyphenyl) hexafluoropropane 2,2′-bis (4-amino-3,5-dihydroxyphenyl) hexafluoropropane and the like. These diamines may be used alone or in combination of two or more. Among these diamines, 4,4′-diaminobiphenyl-3,3′-diol, 2,2′-bis (3-amino-), from the viewpoints of solubility, insulation reliability, polymerization rate, and availability of polyimide. 4-Hydroxyphenyl) hexafluoropropane is preferred.

  As content of the diamine represented by the said General formula (5), it is preferable that it is 5 mol%-30 mol% with respect to all the diamine, and it is more preferable that it is 10 mol%-25 mol%. If the content of the diamine represented by the general formula (5) is 5 mol% or more, the alkali solubility is improved, and if it is 30 mol% or less, the solvent solubility is improved.

  In addition to the tetracarboxylic dianhydride, a conventionally known tetracarboxylic dianhydride may be used in combination as long as the effects of the present invention are achieved. Examples of such tetracarboxylic dianhydrides include pyromellitic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3- Dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (3 , 4-Dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 1,3-dihydro -1,3-dioxo-5-isobenzofurancarboxylic acid-1,4-phenylene ester, 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydrona Talen-1,2-dicarboxylic anhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3,5,6 -Pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2- Bis (4- (3,4-dicarboxyphenoxy) phenyl) hexafluoropropane dianhydride, 2,2-bis (4- (3,4-dicarboxybenzoyloxy) phenyl) hexafluoropropane dianhydride, 2 , 2′-bis (trifluoromethyl) -4,4′-bis (3,4-dicarboxyphenoxy) biphenyl dianhydride and the like, and cyclobutanthate Carboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5,6-cyclohexanetetracarboxylic dianhydride, 5- (2,5-dioxotetrahydro- 3-furanyl) -3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo [2,2,2] oct-7-ene-2,3,5,6 tetracarboxylic dianhydride And aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. These tetracarboxylic dianhydrides may be used alone or in combination of two or more. Among these tetracarboxylic dianhydrides, 4,4'-oxydiphthalic dianhydride is preferably used from the viewpoint of flexibility, solubility, insulation reliability and polymerization rate of polyimide.

  Moreover, conventionally well-known diamino can be used together with the said diamine in the range with the effect of this invention. Examples of such diamines include 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 1,3-bis (3-amino Phenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, bis (3- (3-aminophenoxy) phenyl) ether, bis (4- (4-aminophenoxy) phenyl) ether, 1,3-bis (3- (3-aminophenoxy) phenoxy) benzene, 1,4-bis (4- (4-aminophenoxy) phenoxy) benzene, bis (3- (3- (3-aminophenoxy) phenoxy) phenyl) ether, Bis (4- (4- (4-aminophenoxy) phenoxy) phenyl) ether, 1,3-bis ( -(3- (3-aminophenoxy) phenoxy) phenoxy) benzene, 1,4-bis (4- (4- (4-aminophenoxy) phenoxy) phenoxy) benzene, 4,4'-bis (3-aminophenoxy) ) Biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ] Propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) Phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, bis (3-amino Phenyl) sulfide, bis (4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, bis (4-aminophenyl) sulfoxide, bis (3-aminophenyl) sulfone, bis (4-aminophenyl) sulfone, 2 , 2-bis [4- (3-aminophenoxy) phenyl] butane, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω -Bis (4-aminobutyl) polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, and the like.

  Among these diamines, polyoxyethylene diamine, polyoxypropylene diamine, and other polyoxyalkylene diamines containing oxyalkylene groups having different numbers of carbon chains may be used to reduce the elastic modulus of the cured adhesive resin. preferable. Examples of polyoxyalkylene diamines include polyoxyethylene diamines such as Jeffamine ED-600, ED-900, ED-2003, EDR-148, and HK-511 manufactured by Huntsman, Jeffamine D-230, D-400, Polyoxypropylene diamines such as D-2000, D-4000, polyetheramine D-230, D-400, D-2000 manufactured by BASF, and poly, such as Jeffamine XTJ-542, XTJ-533, XTJ-536 Examples thereof include a diamine having a tetramethyleneethylene group. Further, when improving the solubility of the uncured adhesive resin, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω -Bis (4-aminobutyl) polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, α- (2-aminopropyl) -Omega-amino poly (oxypropylene) etc. can be used.

  In order to reduce the elastic modulus of the cured adhesive resin, the diamine content is preferably 25 mol% to 65 mol%, more preferably 40 mol% to 65 mol%, based on the total diamine. It is more preferable. When the content of the diamine is 25 mol% or more, flexibility and solvent solubility are improved, and when it is 65 mol% or less, alkali solubility is improved.

  Moreover, a hydroxyl group and / or a carboxyl group can be introduce | transduced into a polyimide by using the following diamine. Such diamines include 2,5-diaminophenol, 3,5-diaminophenol, 4,4 ′-(3,3′-dihydroxy) diaminobiphenyl, 4,4 ′-(2,2 '-Dihydroxy) diaminobiphenyl, 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 3-hydroxy-4-aminobiphenyl (HAB), 4,4'-(3,3'- And dicarboxy) diphenylamine, methylenebisaminobenzoic acid (MBAA), 2,5-diaminobenzoic acid (DABA), 3,3′-dicarboxy-4,4′-diaminodiphenyl ether, and the like.

  Next, a method for producing polyimide will be described. As a method for producing polyimide, all methods for producing polyimide including known methods can be applied. Among these, it is preferable to perform the reaction in an organic solvent. Examples of the solvent used for the synthesis of polyimide include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1 , 3-dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, ethyl benzoate and the like. These may be used alone or in combination of two or more.

  In the present embodiment, it is required that there is no blister due to outgas in the heat curing step of the cured adhesive resin 103 after the formation of the through via hole 106 and / or the blind via hole 107. In addition, when components are mounted on a flexible wiring board, there is no need for blistering due to outgas during solder reflow, and reliability in a thermal cycle test is required. From these viewpoints, the residual solvent amount after curing of the adhesive resin cured product 103 is preferably 0.5% by mass or less. Further, the residual solvent amount after curing of the cured adhesive resin 103 is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and 0.05% by mass or less. More preferably it is.

  From the above viewpoint, the solvent used for the polymerization of polyimide is preferably a solvent having excellent drying properties. Examples of the solvent having excellent drying properties include solvents that do not contain an amide structure. Among these, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, excellent in volatility, Methyl benzoate, ethyl benzoate and the like are preferable.

  When a polyimide having a amide structure such as N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone is used in the synthesis of polyimide, the polyimide and amide structure are also used under reduced pressure conditions. It is difficult to reduce the residual amount of the solvent to 0.5% or less due to hydrogen bonding between the solvent and the solvent. On the other hand, when a polyimide is polymerized using a solvent having an amide structure, a poor solvent is added after the polymerization to precipitate a polymer, and the precipitated polymer is recovered and dried, and then re-converted into a highly volatile solvent. It may be used after being dissolved.

  As a density | concentration of the reaction raw material in the synthesis | combination of a polyimide, it is 2 mass%-80 mass% normally, and it is preferable that it is 20 mass%-50 mass%.

  The molar ratio of tetracarboxylic dianhydride and diamine used for the synthesis of polyimide is in the range of 0.8 to 1.2. Within this range, the molecular weight of the polyimide can be increased, and the elongation and the like are also improved. The molar ratio of tetracarboxylic dianhydride and diamine is preferably 0.9 to 1.1, and more preferably 0.92 to 1.07.

  The weight average molecular weight of the polyimide is preferably 5000 or more and 100,000 or less. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography using polystyrene having a known number average molecular weight as a standard. The weight average molecular weight is more preferably from 10,000 to 60,000, and most preferably from 15,000 to 50,000. When the weight average molecular weight is 5,000 or more and 100,000 or less, the elongation of the cured adhesive resin layer obtained using the adhesive resin is improved, and the mechanical properties are improved. Further, it can be applied without spreading to a desired film thickness when the uncured adhesive resin 103 ′ is applied.

  Specifically, the polyimide is synthesized by the following method. First, the polyimide precursor which consists of a polyamic acid structure is manufactured by carrying out the polycondensation reaction of the reaction raw material within the range of room temperature to 80 degreeC. Next, the polyimide precursor is preferably heated to 100 ° C. to 400 ° C. to imidize, or chemically imidized using an imidizing agent such as acetic anhydride, thereby repeating unit structure corresponding to polyamic acid. Is obtained. In the case of imidization by heating, in order to remove by-product water, dehydration is carried out under reflux using a Dean-Stark type dehydrator in the presence of an azeotropic agent (preferably toluene or xylene). Is also preferable.

  Moreover, it is also preferable to obtain a polyimide by carrying out the reaction at 80 ° C. to 220 ° C. to advance both the generation of the polyimide precursor and the thermal imidization reaction. That is, a diamine component and an acid dianhydride component are suspended or dissolved in an organic solvent, and reacted under heating at 80 ° C. to 220 ° C. to cause both generation of a polyimide precursor and dehydration imidization. It is also preferable to obtain polyimide.

  Moreover, the terminal of the polymer main chain of the polyimide precursor can be end-capped with an end-capping agent made of a monoamine derivative or a carboxylic acid derivative. By sealing the terminal of the polymer main chain of polyimide, the storage stability derived from the terminal functional group is excellent.

  Examples of the end capping agent comprising a monoamine derivative include aniline, o-toluidine, m-toluidine, p-toluidine, 2,3-xylidine, 2,6-xylidine, 3,4-xylidine, and 3,5-xylidine. O-chloroaniline, m-chloroaniline, p-chloroaniline, o-bromoaniline, m-bromoaniline, p-bromoaniline, o-nitroaniline, p-nitroaniline, m-nitroaniline, o-aminophenol P-aminophenol, m-aminophenol, o-anisidine, m-anisidine, p-anisidine, o-phenetidine, m-phenetidine, p-phenetidine, o-aminobenzaldehyde, p-aminobenzaldehyde, m-aminobenzaldehyde, o-aminobenzonitrile, p-aminobenzonitrile Ryl, m-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl, 2-aminophenylphenyl ether, 3-aminophenylphenyl ether, 4-aminophenylphenyl ether, 2-aminobenzophenone, 3 -Aminobenzophenone, 4-aminobenzophenone, 2-aminophenyl phenyl sulfide, 3-aminophenyl phenyl sulfide, 4-aminophenyl phenyl sulfide, 2-aminophenyl phenyl sulfone, 3-aminophenyl phenyl sulfone, 4-aminophenyl phenyl sulfone , Α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol, 5-amino-1-naphthol, 2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino Aromatic monoamines such as 2-naphthol, 7-amino-2-naphthol, 8-amino-1-naphthol, 8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene Of these, derivatives of aniline are preferably used. These may be used alone or in combination of two or more.

  Examples of the terminal blocking agent made of a carboxylic acid derivative mainly include carboxylic anhydride derivatives. Examples of the terminal blocking agent comprising a carboxylic acid derivative include phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl ether anhydride, 3,4-dicarboxyphenyl phenyl ether anhydride, 2,3-biphenyl dicarboxylic acid anhydride, 3,4-biphenyl dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxy Phenylphenyl sulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride, 1,2-naphthalenedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic acid anhydride, 1,8-naphthalenedicarboxylic anhydride, 1,2-a Tiger Sen dicarboxylic acid anhydride, 2,3-anthracene dicarboxylic acid anhydride, 1,9-aromatic dicarboxylic acid anhydrides such as anthracene dicarboxylic acid anhydride. Of these aromatic dicarboxylic acid anhydrides, phthalic anhydride is preferably used. These may be used alone or in combination of two or more.

  You may use the polyimide solution obtained by superposition | polymerization as it is, without removing a solvent. Moreover, it can also be set as an adhesive resin varnish by adding a required solvent, an additive, etc.

  In the manufacturing method of the multilayer flexible wiring board according to the present embodiment, the uncured adhesive resin layers 103a ′ and 103b ′ are dissolved and removed through the conformal mask formed on the external conductive layers 104a and 104b, and the blind via hole 107 is formed. Form. After forming the blind via hole 107, the uncured adhesive resin layers 103a 'and 103b' are cured by heating. Therefore, the uncured adhesive resin layers 103a ′ and 103b ′ before heating are required to have sufficient alkali solubility, and the cured adhesive resin layers 103a and 103b after heat curing are alkali resistant (alkali solubility). Reduction) is required. For this reason, in the present embodiment, the reactive compound is 120 ° C. or lower, preferably 100 ° C. or lower, and the reaction with the hydroxyl group of the hydroxyl group-containing resin is slow, and is reacted at 150 ° C. or higher, preferably 170 ° C. or higher. Is used so that the uncured adhesive resin layers 103a and 103b are sufficiently cured.

  Examples of the reactive compound include an oxazoline compound, a benzoxazine compound, an epoxy compound, an oxetane compound, and the like. Among these, an oxazoline compound, a benzoxazine compound, and an oxetane compound are preferable, and an oxazoline compound that does not by-produce a hydroxyl group by a reaction with a hydroxyl group of a hydroxyl group-containing resin is particularly preferable. Here, the oxazoline compound is a compound having at least one oxazoline group in the molecule. Moreover, as an oxazoline compound, what has two or more oxazoline groups in a molecule | numerator from a viewpoint of sealing the hydroxyl group of a hydroxyl-containing compound and forming bridge | crosslinking between hydroxyl-containing compounds is preferable.

  In the present embodiment, an appropriate amount of a reactive compound (for example, an oxazoline compound) is added to a hydroxyl group-containing resin (for example, polyimide) having a hydroxyl group, and dried at an appropriate temperature. Accordingly, the uncured adhesive resin layers 103a and 103b are dissolved and removed by a 3% by mass sodium hydroxide aqueous solution at a predetermined temperature (for example, 48 ° C.) to form through via holes, blind via holes, or through holes. It becomes possible. In addition, the hydroxyl group of the hydroxyl group-containing resin reacts with the reactive compound (for example, the oxazoline group of the oxazoline compound) by a heat treatment for 1 hour at a predetermined temperature (for example, 180 ° C.), and can exhibit resistance to an aqueous alkali solution. . Further, when a reaction compound containing a plurality of oxazoline groups is used, cross-linking is formed between the molecules of the hydroxyl group-containing compound (for example, polyimide).

  Examples of the oxazoline compound include 1,3-bis (4,5-dihydro-2-oxazolyl) benzene, K-2010E, K-2020E, K-2030E, 2,6-bis (4- Isopropyl-2-oxazolin-2-yl) pyridine, 2,6-bis (4-phenyl-2-oxazolin-2-yl) pyridine, 2,2′-isopropylidenebis (4-phenyl-2-oxazoline), 2,2'-isopropylidenebis (4-tertiarybutyl-2-oxazoline) and the like can be mentioned. These oxazoline compounds may be used alone or in combination of two or more.

  As the addition amount of the oxazoline compound, the molar ratio of the hydroxyl group of the hydroxyl group-containing compound to the oxazoline group of the oxazoline compound is preferably hydroxyl group / oxazoline group = 0.5-4, and preferably 0.7-3. More preferred. If the hydroxyl group / oxazoline group = 0.5 or more, the flexibility and heat resistance of the uncured adhesive resin layers 103a and 103b are improved. If the hydroxyl group / oxazoline group = 4 or less, the uncured adhesive resin layer 103a. , 103b is improved.

  The uncured adhesive resin becomes a cured adhesive resin by heating. Although it does not restrict | limit especially about heating, From a viewpoint made soluble in an antkari aqueous solution, it is preferable to heat for 1 minute-60 minutes at 50 to 140 degreeC. Further, heating at a high temperature (for example, 160 ° C. to 200 ° C.) mainly causes hydroxyl group sealing and crosslinking reaction, and becomes insoluble in an alkaline aqueous solution.

  In addition, the uncured adhesive resin layers 103a and 103b can remove volatile components such as solvents and residual monomers sufficiently and make them soluble in an antkari aqueous solution at 50 ° C. to 140 ° C. for 1 minute from the viewpoint of making them soluble in an antkari aqueous solution. Heating for ~ 60 minutes is preferred. Since the uncured adhesive resin layers 103a and 103b heated at 50 to 140 ° C. for 1 to 60 minutes are soluble in the antkari aqueous solution, the laser drilling process used in the manufacture of the flexible printed wiring board is not necessary, It can be used as an adhesive resin 103 that can process blind via holes with an antkari aqueous solution.

  After forming the blind via hole with the ant potassium solution, the remaining uncured adhesive resin layers 103a and 103b are heated at a higher temperature (for example, 160 ° C. to 200 ° C.), thereby mainly between the hydroxyl group-containing compound and the reactive compound. A cross-linking reaction occurs to form the cured adhesive resin layers 103a and 103b, which are insoluble in the alkaline aqueous solution. Specifically, depending on the film thickness of the uncured adhesive resin layers 103a and 103b to be formed, the maximum temperature is set in the range of 150 ° C. to 220 ° C. with an oven or a hot plate, and air or The crosslinking reaction proceeds by heating in an inert atmosphere such as nitrogen. The heating temperature may be constant over the entire processing time or may be gradually raised.

  Moreover, the adhesive resin varnish which concerns on this Embodiment can also be made to contain a flame retardant from a viewpoint of improving a flame retardance. Although it does not restrict | limit especially as a flame retardant, A halogen-containing compound, a phosphorus-containing compound, an inorganic flame retardant, etc. are mentioned. These flame retardants may be used alone or in combination of two or more.

  Examples of the halogen-containing compound include an organic compound containing chlorine and an organic compound containing bromine. Examples of the halogen-containing compound include pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane tetrabromobisphenol A, and the like.

  Examples of the phosphorus-containing compound include phosphorus compounds such as phosphazene, phosphine, phosphine oxide, phosphate ester, and phosphite ester. In particular, when polyimide is used as the hydroxyl group-containing compound, it is preferable to use phosphazene, phosphioxide or phosphate ester from the viewpoint of compatibility with polyimide.

  As the phosphazene, a cyclic phosphazene having a phenoxy group is preferable, and a cyclic phosphazene having a cyano group or a hydroxyl group in addition to the phenoxy group is more preferable. Further, the cyclic phosphazene having a hydroxyl group and a phenoxy group reduces alkali solubility by reacting the hydroxyl group of the cyclic phosphazene with a reactive compound (for example, the oxazoline group of the oxazoline compound) when the uncured adhesive resin layers 103a and 103b are cured. It is preferable because it can be used. In particular, it is preferable to use a mixture of a cyclic phosphazene having a cyano group in the phenoxy group and a cyclic phosphazene having a hydroxyl group in the phenoxy group.

  Examples of inorganic flame retardants include antimony compounds and metal hydroxides. Examples of the antimony compound include antimony trioxide and antimony pentoxide. By using the antimony compound and the halogen-containing compound in combination, the antimony compound pulls out the halogen atom from the halogen-containing compound at a predetermined temperature (for example, the thermal decomposition temperature range of the plastic) to generate antimony halide. The flame retardancy can be increased. Examples of the metal hydroxide include aluminum hydroxide and magnesium hydroxide.

  Since an inorganic flame retardant does not dissolve in an organic solvent, it is preferable to use a powder having a particle size of 100 μm or less. If the particle size of the powder is 100 μm or less, it is preferable because it is easy to be mixed in the adhesive resin varnish and does not impair the transparency of the cured adhesive resin layers 103a and 103b. In order to further increase the flame retardancy, the particle size of the powder is preferably 50 μm or less, and more preferably 10 μm or less.

  The addition amount of the flame retardant is not particularly limited and is appropriately selected depending on the type of the flame retardant used. Generally, it is used in the range of 5% by mass to 50% based on the content of the hydroxyl group-containing compound.

  When the adhesive resin varnish is used as a coating film, the viscosity and thixotropy are adjusted according to the coating method. If necessary, a filler or a thixotropic agent can be added and used. It is also possible to add additives such as known antifoaming agents, leveling agents and pigments.

  Moreover, the adhesive resin varnish which concerns on this Embodiment can also be made to contain an adhesive material from a viewpoint of improving adhesiveness with a conductive layer. Although it does not restrict | limit especially as an adhesive material, A phenol compound, a nitrogen-containing organic compound, an acetylacetone metal complex etc. are mentioned. Among these, a phenol compound is particularly preferable.

  The adhesive resin varnish may contain an organic solvent in addition to a hydroxyl group-containing compound and a reactive compound. Since the coating is facilitated by dissolving in an organic solvent, it can be preferably used.

  Examples of such organic solvents include amide solvents such as N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone, γ -Lactone solvents such as butyrolactone and γ-valerolactone, sulfur-containing solvents such as dimethyl sulfoxide, diethyl sulfoxide and hexamethyl sulfoxide, phenol solvents such as cresol and phenol, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) And ether solvents such as tetraglyme, dioxane, tetrahydrofuran, butyl benzoate, ethyl benzoate, and methyl benzoate. These organic solvents may be used alone or in combination.

  In the present embodiment, in order to develop the formation property of the blind via hole and the heat resistance of the solder reflow of the multilayer board and the thermal cycle test, the solvent is suppressed while suppressing the reaction between the hydroxyl group-containing compound and the reactive compound. It is necessary to volatilize. When an amide solvent is used, the hydrogen bond between the hydroxyl group of the hydroxyl group-containing compound (for example, polyimide) and the amide solvent is strong, and the amide solvent is less likely to volatilize. Therefore, as an organic solvent used for the adhesive resin varnish, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxane, 1 is a solvent that does not contain an amide structure and has excellent volatility. It is preferable to use solvents such as 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, and ethyl benzoate. Since these solvents can reduce the amount of residual solvent by drying under normal pressure, they are excellent in productivity.

  The adhesive resin varnish may contain a crosslinkable compound having a thermally crosslinkable functional group. The heat crosslinkable compound is not particularly limited as long as it forms a crosslink via a heat crosslinkable functional group, and examples thereof include triazine compounds and benzoxazine compounds.

  As the triazine compound, melamine melamines and melamine cyanurate are preferable. Examples of melamines include melamine derivatives, compounds having a structure similar to melamine, and melamine condensates. Specific examples of melamines include, for example, methylolated melamine, ammelide, ammelin, formoguanamine, guanylmelamine, cyanomelamine, arylguanamine, melam, melem, melon and the like.

  Examples of melamine cyanurates include equimolar reaction products of cyanuric acid and melamines. Moreover, some of the amino groups or hydroxyl groups in the melamine cyanurates may be substituted with other substituents. Among these, melamine cyanurate can be obtained, for example, by mixing an aqueous solution of cyanuric acid and an aqueous solution of melamine, reacting at 90 ° C. to 100 ° C. with stirring, and filtering the generated precipitate, Yes, a commercially available product can be used as it is or after being pulverized into a fine powder.

  The benzoxazine compound may be composed only of monomers, or several molecules may be polymerized into an oligomer state. Moreover, you may use the benzoxazine compound which has a different structure simultaneously. Specifically, bisphenol benzoxazine is preferably used.

  Moreover, the adhesive resin varnish which concerns on this Embodiment can also be used as metal foil with resin by apply | coating on metal foil and drying. In this case, there is no restriction | limiting in particular about the coating method and the drying method of the adhesive resin varnish to the surface of copper foil. For example, an adhesive resin varnish is applied to the surface of a copper foil using an edge coater, gravure coater, spin coater, etc., and is heated and dried in a heating furnace to form an uncured adhesive resin layer on the copper foil. A copper foil is obtained. The film thickness obtained after drying is an average thickness of 5 μm to 50 μm. In order to reduce the solvent in the adhesive resin 103, it is preferable to heat at 50 to 140 ° C. for 1 to 60 minutes at normal pressure or reduced pressure.

  Further, the adhesive resin varnish according to the present embodiment is suitably used as a protective film for the wiring pattern of the wiring board by providing an adhesive resin cured product layer so as to cover the wiring pattern formed on the substrate. be able to.

  As described above, in the flexible wiring board according to the present embodiment, the adhesive resin containing an alkali-soluble resin is cured on the inner wall of the via hole (through via hole and / or blind via hole) for interlayer connection of the flexible wiring board. A conductive particle layer is formed on the physical layer to electrically connect the conductive layers. As a result, the cost for forming via holes can be greatly reduced, roll-to-roll production can be facilitated, production lead time can be greatly reduced, circuit quality is excellent, and double-sided flexible wiring boards and multilayer flexible have high connection reliability. Wiring boards and rigid / flexible wiring boards can be provided. Further, in the conventional method for manufacturing a flexible substrate, there is a concern of a defective via hole defect (serious defect) due to smear, but according to the present embodiment, a smear does not occur and a via hole having high connection reliability can be obtained. .

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples made to clarify the effects of the present invention, but the present invention is not limited to these examples.

[Preparation Example 1]
A three-necked separable flask was equipped with a nitrogen condenser, a thermometer, and a ball condenser equipped with a moisture separation trap. At oil bath room temperature, triethylene glycol dimethyl ether (22.5 g), γ-butyrolactone (52.5 g), toluene (20.0 g), 4,4′-oxydiphthalic dianhydride (ODPA) 1.00 g, both ends 35.00 g of acid dianhydride-modified silicone (X-22-2290AS, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred until uniform. Furthermore, after adding 14.2Og of 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) little by little, it heated up to 180 degreeC and heated for 2 hours. During the reaction, by-product water was azeotroped with toluene and dehydrated under reflux using a ball-mounted condenser equipped with a water separation trap. After draining by-product water, the reflux was stopped, toluene was completely drained, and the mixture was cooled to room temperature. Next, the product was pressure filtered through a 5 μm filter to obtain a polyimide A varnish. The weight average molecular weight was 27,000.

  69% by mass of polyimide A, 6% by mass of 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) as an oxazoline group-containing compound, and 25% by mass of FP300 manufactured by Fushimi Pharmaceutical Co., Ltd. as a flame retardant An adhesive resin varnish was prepared so that

[Preparation Example 2]
In a glass reaction kettle equipped with a stirrer, a condenser, and a nitrogen gas introduction tube, phenol 404.2 g (4.30 mol), 4,4′-di (chloromethyl) biphenyl 150.70 g (0.6 mol) Were added and reacted at 100 ° C. for 3 hours, followed by addition of 28.57 g (0.4 mol) of 42% formalin aqueous solution, and then reacted at 100 ° C. for 3 hours. Meanwhile, the methanol produced was distilled off. After completion of the reaction, the obtained reaction solution was cooled and washed with water three times. The oil layer was separated, and unreacted phenol was removed by distillation under reduced pressure to obtain 251 g of phenol novolac resin.

  62.5% by mass of phenol novolac resin, 12.5% by mass of 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) as a compound containing an oxazoline group, and Fushimi Pharmaceutical Co., Ltd. as a flame retardant The adhesive resin was adjusted so that the amount of FP300 produced was 25% by mass, and N-methylpyrrolidone was diluted with 40 g as a solvent to prepare an adhesive resin varnish.

[Preparation Example 3]
A three-necked separable flask was equipped with a nitrogen condenser, a thermometer, and a ball condenser equipped with a moisture separation trap. In an oil bath room temperature, 344 g of 1,3-dimethyl-2-imidazolidinone (DMI), 90 g of toluene, 78.4 g of dimethyl sulfoxide, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane ( (6FAP) 48.8 g and polyalkyl ether diamine Baxodur (registered trademark) EC302 (manufactured by BASF) 112.8 g were added and stirred until uniform. Further, 120 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) was added little by little, and then the temperature was raised to 180 ° C. and heated for 3 hours. During the reaction, by-product water was azeotroped with toluene and dehydrated under reflux using a ball-mounted condenser equipped with a water separation trap. After draining by-product water, the reflux was stopped, toluene was completely drained, and the mixture was cooled to room temperature. Next, the product was subjected to pressure filtration with a 5 μm filter to obtain a polyimide B varnish. The weight average molecular weight was 28,000.

  This polyimide B varnish was poured into distilled water and reprecipitated, and the resulting precipitate was dried with a vacuum dryer to obtain a solid material of polyimide B. A mixed solvent of γ-butyrolactone: dimethylsulfoxide (DMSO) = 80: 20 was added to the solid material of polyimide B so that the solid content of the adhesive resin was 40% by mass, and the total solid content of the adhesive resin was Is 100% by mass, polyimide A in the adhesive resin is 60% by mass, and 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) is 15 as the compound containing an oxazoline group. Prepare an adhesive resin varnish with a mass% of FP300 and FP400 made by Fushimi Pharmaceutical Co., Ltd. as flame retardants and 1% by weight of Irganox 245 (IRG245, manufactured by BASF) as antioxidants, respectively. did.

[Evaluation of connection reliability]
A wiring circuit (daisy chain) in which two conductive layers are electrically connected to each other by electroplating through a through via hole or a blind via hole is formed on a flexible wiring board, and this is subjected to a temperature cycle test (IPC-TM650 2) of −40 ° C. to 120 ° C. , 6 and 6). As evaluation methods, the case where the connection resistance change rate is ± 10% or less is 500 cycles or more, ◎ is 250 cycles or more and less than 500 cycles, and ２５０ is 250 cycles or less.

<Elastic modulus>
The laminate of about 25 μm was cured in the air at 180 ° C. for 1 hour in a drier (SPHH-10 l, manufactured by ESPEC), and then the copper foil portion was dissolved with a ferric chloride aqueous solution. After washing with distilled water, the film was obtained by drying at room temperature for 1 day. The obtained film was cut out into 5 mm x 100 mm, and it was set as the test piece. The obtained test piece was measured with a tensile tester (RTG-1210 / manufactured by A & D) to calculate the tensile modulus. The case where the tensile modulus was 0.05 GPa or more and 1.5 GPa or less was rated as ◎, the case where it was less than 0.05 GPa and 1.5 GPa or more and 3 GPa or less was rated as ○, and the case where it was above 3.0 GPa was rated as x.

[Example 1]
(Double-sided flexible wiring board with through via holes)
The adhesive resin varnish obtained from Preparation Example 1 was applied onto a 12 μm thick electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) using a bar coater, and then 30 minutes in an oven heated to 95 ° C. Drying treatment was performed to form an uncured adhesive resin layer. An electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) was placed on the surface of the uncured adhesive resin layer, and a laminate was further sandwiched between the release films from both sides. Using a vacuum press device (Kitakawa Seiki Co., Ltd.) with a 50% hardness heat-resistant silicon rubber containing glass cloth inside, on both upper and lower surface plates, the silicon rubber surface temperature was preheated. In the state, after putting the said laminated body and evacuating, pressure 1MPa was pressurized and the laminated body was produced.

  Next, after laminating DF on the copper foil on both sides using the above laminate, the copper foil at a predetermined position is removed by exposure / development and etching, and a conformal mask is formed on the corresponding part on both sides did. In this step, the deviation between the copper foil etching portions on both sides was minimized (when the via hole diameter is 100 μm, it is 20 μm or less).

  Thus, the double-sided flexible printed circuit board produced in Example 1 is a conventional double-sided flexible wiring board that is processed one hole at a time (in the case of drilling, several sheets are stacked) using a drilling machine or a laser machine. Unlike the above manufacturing method, it was possible to punch holes instantaneously by passing through exposure and development processes. For this reason, continuous automated production by roll-to-roll is also easy.

  Next, a 3% sodium hydroxide aqueous solution heated to 50 ° C. is sprayed on the uncured adhesive resin layer exposed at the site where the copper foil has been removed to remove the uncured adhesive resin layer, and through via holes Formed. Next, the uncured adhesive resin layer was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace to obtain a cured adhesive resin layer. Resin residue was not observed on the wall surface of the obtained through via hole, the formation of the through via hole was good, and the desmear process was unnecessary.

  Next, the same penetration via hole plating process as the conventional double-sided flexible wiring board was performed. First, carbon fine particles were adhered to the cured adhesive resin layer on the inner wall of the through via hole to form a conductive particle layer. As a forming method, the film was immersed in a carbon black dispersion having an average particle diameter of 100 nm at 25 ° C. for 30 seconds, and then the dispersion wrinkles were removed with an acid-based aqueous solution. Thereafter, electrolytic copper plating was applied to complete electrical connection on both sides. Next, the same circuit formation process as the conventional double-sided flexible wiring board was performed. The subsequent steps were performed in the same manner as in the conventional manufacturing method for flexible substrates.

  It was confirmed that the double-sided flexible substrate produced in Example 1 was able to form an electroplated layer on the inner wall surface of the via hole without a thickness defect even without desmear treatment with a strong alkaline chemical. The via hole connection reliability was also excellent.

[Comparative Example 1]
Using the resin composition obtained from Adjustment Example 1 in the same manner as in Example 1, plating treatment was performed on the double-sided flexible substrate in which the through via hole was formed. First, an electroless copper plating layer was formed on the cured adhesive resin layer on the inner wall of the through via hole. As a forming method, after depositing and activating the palladium catalyst, an electroless copper plating layer of about 1 μm was formed in an electroless copper plating treatment bath (manufactured by Uemura Kogyo). Subsequently, electrolytic copper plating treatment was performed to complete the electrical connection on both sides.

  Next, the circuit formation process similar to the conventional double-sided flexible wiring board was performed. The subsequent steps were performed in the same manner as in the conventional manufacturing method for flexible substrates.

  The double-sided flexible board produced in Comparative Example 1 did not require desmear treatment with strong alkali, but when the cross-sectional structure of the through via hole was confirmed, a formation defect was found in the electrolytic copper plating layer, and the connection reliability of the through via hole was confirmed. Was x.

[Example 2]
(Double-sided flexible wiring board with blind via holes)
In the same manner as in Example 1, a laminate was prepared using the adhesive resin varnish of Preparation Example 1, and after laminating a dry film on the copper foils on both sides, exposure / development and etching were performed at predetermined positions. The copper foil was removed, and a conformal mask with a diameter of 150 μmφ was generally formed at a predetermined part on one side.

  Next, 3% sodium hydroxide aqueous solution heated to 50 ° C. is sprayed onto the exposed uncured adhesive resin layer at the site where the copper foil has been removed to remove the uncured adhesive resin layer, and the blind via hole Formed. Next, the uncured adhesive resin layer was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace to obtain a cured adhesive resin layer. Resin residue was not observed on the wall surface and bottom of the obtained blind via hole, the formation of the blind via hole was good, and the desmear process was unnecessary. Next, blind via-hole plating similar to the conventional double-sided flexible wiring board was performed.

  First, carbon fine particles were adhered to the cured adhesive resin layer on the inner wall of the blind via hole to form a conductive particle layer. As a forming method, the film was immersed in a carbon black dispersion having an average particle diameter of 100 nm at 25 ° C. for 30 seconds, and then the dispersion wrinkles were removed with an acid-based aqueous solution. Thereafter, electrolytic copper plating was applied to complete electrical connection on both sides. Next, the same circuit formation process as the conventional double-sided flexible wiring board was performed. Subsequent steps were performed in the same manner as the conventional method for manufacturing a double-sided flexible wiring board.

  It was confirmed that the double-sided flexible substrate produced in Example 2 was able to form an electroplated layer on the inner wall surface of the blind via hole without a thickness defect even without desmear treatment with a strong alkaline chemical solution. The via hole connection reliability was also excellent.

[Example 3]
(Manufacturing method of multilayer flexible wiring board)
Espanex M (manufactured by Nippon Steel Chemical Co., Ltd., copper foil thickness 12 μm, insulating resin layer thickness 20 μm) was used as the double-sided flexible wiring board as the core substrate. The double-sided flexible wiring board was formed with a diameter of 100 μm by drilling and copper plating. Further, a copper wiring circuit (28 μm thickness) having a minimum pitch of 130 μm was formed.

  In the oven, the laminate was coated with the adhesive resin varnish obtained from Preparation Example 1 on a 12 μm thick electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) using a bar coater and then heated to 95 ° C. And dried for 12 minutes. This laminate was placed on the top and bottom surfaces of the core substrate, and a laminate sandwiched between release films from both sides was prepared.

  Next, a 50% hardness heat-resistant silicon rubber containing glass cloth inside is bonded to the entire surface of the upper and lower double-sided surface plates. Using a vacuum press machine, the silicon rubber surface temperature is preheated and laminated. The body was put in and evacuated and then pressurized at a pressure of about 1 MPa to produce a laminate.

  Next, for the connection between the copper foil of the laminate and the copper foil of the core substrate, after laminating a dry film on the copper foil of the laminate, the copper foil at a predetermined position by exposure / development and etching And a conformal mask with a diameter of 100 μm was formed at a site where a blind via hole was necessary.

  Next, a 3% sodium hydroxide aqueous solution heated to 50 ° C. is sprayed on the exposed uncured adhesive resin layer for about 30 seconds on the exposed portion of the copper foil to remove the uncured adhesive resin layer. Blind via holes were formed.

  Next, the alkali-soluble resin of the uncured adhesive resin layer was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace. Resin residue was not observed on the wall surface and bottom of the obtained blind via hole, and the formation of the blind via hole was good, and the desmear process using an aqueous potassium permanganate solution or the like was unnecessary.

  Next, in order to make an electrical connection with the core substrate, a plating process for blind via holes was performed. First, carbon fine particles were attached to the cured adhesive resin layer on the inner wall of the blind via hole to form a conductive particle layer. As a forming method, the film was immersed in a carbon black dispersion having an average particle diameter of 100 nm at 25 ° C. for 30 seconds, and then the dispersion wrinkles were removed with an acid-based aqueous solution. Thereafter, electrolytic copper plating was applied to a thickness of about 15 μm to complete the electrical connection on both sides.

  It was confirmed that the multilayer flexible substrate produced in Example 3 was able to form an electroplating layer on the inner wall surface of the blind via hole without a thickness defect even without desmear treatment with a strong alkaline chemical. The connection reliability between via holes was also excellent.

  Next, the same circuit formation process as the conventional multilayer flexible wiring board was performed. The subsequent steps were performed in the same manner as the conventional method for manufacturing a flexible wiring board.

[Example 4]
A multilayer flexible wiring board was produced using the adhesive resin varnish obtained from Adjustment Example 2 in the same manner as in Example 3. Although the film thickness defect of the electroplating layer between the blind via holes was not recognized, the connection reliability was also excellent.

[Example 5]
A multilayer flexible wiring board was produced using the adhesive resin varnish obtained from Adjustment Example 2 in the same manner as in Example 3. The film thickness defect of the electroplating layer between the blind via holes was not particularly recognized, and the connection reliability was good.

[Comparative Example 2]
Using the adhesive resin varnish obtained from Adjustment Example 1 in the same manner as in Example 3, plating was performed on the multilayer flexible substrate on which blinders were formed. First, an electroless copper plating layer was formed on the cured adhesive resin layer on the inner wall of the blind via hole. As a forming method, after depositing and activating the palladium catalyst, an electroless copper plating layer of about 1 μm was formed in an electroless copper plating treatment bath (manufactured by Uemura Kogyo). Subsequently, electrolytic copper plating treatment was performed to complete the electrical connection on both sides.

  Next, the circuit formation process similar to the conventional multilayer flexible wiring board was performed. The subsequent steps were performed in the same manner as in the conventional manufacturing method for flexible substrates.

  The multilayer flexible substrate produced in Comparative Example 2 did not require desmear treatment with strong alkali, but as a result of checking the cross-sectional structure of the blind via hole, some formation defects were found in the gap between the copper wiring layer on the external substrate side and the via hole. Connection reliability was x.

[Example 6]
(Multilayer flexible wiring board with flexible parts using blind via holes)
The double-sided flexible wiring board produced in Example 3 was used as the core substrate. The laminate to be laminated on the core substrate was obtained by applying the adhesive resin varnish obtained in Preparation Example 1 onto a 12 μm thick electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) using a bar coater, and then heating to 110 ° C. Obtained by drying in a warm oven for 12 minutes. This laminate was placed on the top and bottom surfaces of the core substrate, and a laminate sandwiched between release films from both sides was prepared.

  Next, a 50% hardness heat-resistant silicon rubber containing glass cloth inside is bonded to the entire surface of the upper and lower double-sided surface plates, with the silicon rubber surface temperature heated in advance using a vacuum press device. The laminate was put in and evacuated, and then pressurized at a pressure of about 1 MPa to produce a laminate.

  Next, for the connection between the copper foil of the laminate and the copper foil of the core substrate, after laminating a dry film on the copper foil of the laminate, the copper foil at a predetermined position by exposure / development and etching Then, a 150 μmφ conformal mask was formed at a site where a blind via hole was required. At the same time, the copper foil was removed in the same process for the part to be the flexible part.

  Next, a 3% sodium hydroxide aqueous solution heated to 50 ° C. is sprayed on the exposed uncured adhesive resin layer for about 30 seconds on the exposed portion of the copper foil to remove the uncured adhesive resin layer. The blind via hole was formed and the flexible part alkali-soluble resin was removed.

  Next, by heating at 180 ° C. for 1 hour using a curing and drying furnace, the alkali-soluble resin of the uncured adhesive resin layer was cured to obtain a cured adhesive resin layer. Resin residue was not observed on the wall surface and bottom of the obtained blind via hole, and the formation of the blind via hole was good, and the desmear process using an aqueous potassium permanganate solution or the like was unnecessary.

  Next, in order to establish electrical connection between the copper foil of the laminate and the copper foil of the core substrate, a plating process for blind via holes was performed. First, carbon fine particles were attached to the cured adhesive resin layer on the inner wall of the blind via hole to form a conductive particle layer. As a forming method, the film was immersed in a carbon black dispersion having an average particle diameter of 100 nm at 25 ° C. for 30 seconds, and then the dispersion wrinkles were removed with an acid-based aqueous solution. Thereafter, electrolytic copper plating was applied to complete electrical connection on both sides. At the same time, copper plating was applied to the flexible film on the base film.

  Next, the circuit formation process similar to the conventional multilayer flexible wiring board was performed. In this step, the copper plating attached to the flexible part was simultaneously removed by etching to form a structure in which the outer layer was removed. The subsequent steps were performed in the same manner as in the conventional method for manufacturing a flexible wiring board.

  There was no particular film thickness defect in the electroplated layer between the blind via holes produced in Example 6, and the connection reliability was also excellent.

  The results of Examples 1 to 6, Comparative Example 1 and Comparative Example 2 are shown in Table 1 below.

  As can be seen from Table 1, when the conductive particle layer is provided in the via hole, it can be seen that connection reliability is obtained (Examples 1 to 6). On the other hand, it can be seen that when the conductive particle layer is not provided, the connection reliability is lowered (Comparative Example 1 and Comparative Example 2).

  In addition, the double-sided flexible wiring board according to Example 1 and Example 2 and the multilayer flexible wiring board according to Example 3 and Example 6 could be punched instantaneously by passing through the exposure / development process. . For this reason, continuous automated production by roll-to-roll is also easy. Moreover, the multilayer flexible wiring board according to Example 6 was able to perform both the via hole forming step and the dry film peeling step. For this reason, production efficiency could be greatly improved. By these, the flexible wiring board which concerns on Example 1- Example 6 is the conventional double-sided flexible which processes a hole one by one (it piles up several sheets in the case of a drill process) using a drilling drill machine or a laser processing machine. The production efficiency was greatly improved compared to the method of manufacturing the wiring board.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  INDUSTRIAL APPLICABILITY The present invention has an effect of providing a flexible wiring board excellent in connection reliability between conductive layers, and can be suitably used particularly as a double-sided flexible wiring board, a multilayer flexible wiring board, and a rigid / flexible wiring board. Yes, it can be used as various electronic components.

11, 21, 101, 103a, 103b Adhesive resin cured product layer 11 ′, 21 ′, 101 ′, 103a ′, 103b ′ Adhesive resin cured product layer 12a, 12b, 22a, 22b Conductive layer 13, 106 Through-via hole 13a , 24a, 106a, 107a Conductive particle layer 14, 23 Conformal mask 24 107 Blind via hole 100 Multilayer flexible wiring board 100a Rigid part 100b Flexible part 102a, 102b Internal conductive layer 103 Adhesive resin cured product 103 'Uncured adhesive resin 104a, 104b External conductive layer 105 Cover coat 110 Double-sided flexible wiring board

Claims (3)

  A first conductive layer, a second conductive layer provided on the first conductive layer via an adhesive resin cured product, and a via hole provided between the first conductive layer and the second conductive layer; A conductive fine particle layer provided so as to cover at least the cured adhesive resin in the via hole and electrically connecting the first conductive layer and the second conductive layer. Flexible wiring board.   The flexible wiring board according to claim 1, wherein the cured adhesive resin has an elastic modulus of 0.05 GPa or more and less than 3.0 GPa.   The flexible wiring board according to claim 1, wherein the conductive particle layer has a thickness of 0.01 μm or more and 10 μm or less.

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